Wavelength division multiplexed (WDM) optical communication systems (referred to as “WDM systems”) are systems in which multiple optical signals, each having a different wavelength, are combined onto a single optical fiber using an optical multiplexer circuit (referred to as a “multiplexer”). Such systems may include a transmitter circuit, such as a transmitter (Tx) photonic integrated circuit (PIC) having a transmitter component to provide a laser associated with each wavelength, a modulator configured to modulate the output of the laser, and a multiplexer to combine each of the modulated outputs (e.g., to form a combined output or WDM signal).
A WDM system may also include a receiver circuit, such as a receiver (Rx) PIC having an optical demultiplexer circuit (referred to as a “demultiplexer”) configured to receive the combined output and demultiplex the combined output into individual optical signals, and receiver components to convert the optical signals into electrical signals, and output the data carried by those electrical signals. Digital optical transmission systems may employ coherent detection to compensate for chromatic dispersion (CD) and polarization mode dispersion (PMD) distortions native in an optical fiber, allowing the use of more complex modulations to increase spectral efficiency and fiber capacity.